Modular PLC discrete output modules are available with solid state AC, solid state DC, and ? type outputs.

• A. Solid state AC
• B. Solid state DC
• C. Relay contact
• D. Analog

Answer: (C)

Discrete output modules in modular PLCs are designed to switch actuators on and off, and they come in three common technologies: solid-state outputs for AC loads, solid-state outputs for DC loads, and relay contact outputs. The missing type is relay contact outputs. Relays provide galvanic isolation between the PLC and the load and can handle higher currents and inductive loads, making them a versatile option when you need robust switching and compatibility with both AC and DC circuits. They are mechanical switches, so they’re slower and wear over time, unlike solid-state options which have no moving parts. Analog outputs aren’t considered discrete on/off outputs, so they don’t fit this category.